at91cap7e ATMEL Corporation, at91cap7e Datasheet - Page 349

• Manufacturer Part Number: at91cap7e
• Description: Customizable Microcontroller
• Manufacturer: ATMEL Corporation

Table 29-2.
29.6.1.2
8549A–CAP–10/08
Source Clock
12 000 000
12 288 000
14 318 180
14 745 600
18 432 000
24 000 000
24 576 000
25 000 000
32 000 000
32 768 000
33 000 000
40 000 000
50 000 000
3 686 400
4 915 200
5 000 000
7 372 800
8 000 000
MHz
Fractional Baud Rate in Asynchronous Mode
Baud Rate Example (OVER = 0)
Expected Baud
The baud rate is calculated with the following formula:
The baud rate error is calculated with the following formula. It is not recommended to work with
an error higher than 5%.
The Baud Rate generator previously defined is subject to the following limitation: the output fre-
quency changes by only integer multiples of the reference frequency. An approach to this
problem is to integrate a fractional N clock generator that has a high resolution. The generator
architecture is modified to obtain Baud Rate changes by a fraction of the reference source clock.
This fractional part is programmed with the FP field in the Baud Rate Generator Register
(US_BRGR). If FP is not 0, the fractional part is activated. The resolution is one eighth of the
clock divider. This feature is only available when using USART normal mode. The fractional
Baud Rate is calculated using the following formula:
38 400
38 400
38 400
38 400
38 400
38 400
38 400
38 400
38 400
38 400
38 400
38 400
38 400
38 400
38 400
38 400
38 400
38 400
Rate
Bit/s
BaudRate
Error
=
1
–
Calculation Result
=
⎛
⎝
ExpectedBaudRate
-------------------------------------------------- -
MCK
ActualBaudRate
12.00
13.02
19.53
20.00
23.30
24.00
30.00
39.06
40.00
40.69
52.08
53.33
53.71
65.10
81.38
6.00
8.00
8.14
⁄
CD
×
16
⎞
⎠
CD
12
13
20
20
23
24
30
39
40
40
52
53
54
65
81
6
8
8
Actual Baud Rate
38 400.00
38 400.00
39 062.50
38 400.00
38 461.54
37 500.00
38 400.00
38 908.10
38 400.00
38 400.00
38 461.54
38 400.00
38 109.76
38 461.54
38 641.51
38 194.44
38 461.54
38 580.25
Bit/s
AT91CAP7E
0.00%
0.00%
1.70%
0.00%
0.16%
2.40%
0.00%
1.31%
0.00%
0.00%
0.16%
0.00%
0.76%
0.16%
0.63%
0.54%
0.16%
0.47%
Error
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